Artificial teeth and dentures are frequently secured to a patient's jaw with apparatus which permits dentures to be removed. Some of these apparatus comprise o-rings for attaching a removable denture to a natural or an implanted fixed root system. Such an apparatus is disclosed, for example, in U.S. Pat. No. 4,193,194 to Dalise. An another apparatus is disclosed in U.S. Pat. No. 4,681,542 to Baum. In both of these systems an o-ring is introduced into a concave retainer cavity. The concave surfaces in the retainer cavity form a relatively sharp edge between the cavity and the rest of an o-ring abutment. Since it is contemplated that the denture may be attched and removed multiple times, excess stress and unwanted wear may be produced in the o-ring as the denture is either attached or removed.